1. Field of the Invention
The invention lies in the semiconductor technology field. More specifically, the invention relates to a semiconductor memory of the random access type having data lines, which can be connected to the local data lines in the memory cell array. The data lines are combined in groups and at least one group or individual data lines of the groups are formed by redundancy data lines. I/O lines (input/output lines) lead from the memory in groups.
In a typical architecture of a 64-Mbit DRAM, the memory area is divided into four quadrants each with a data width of 32 bits. The entire memory comprises 128 bits. The 32-bit-wide data buses of the quadrants are further subdivided into four groups each of 8 bits. The data lines of the data buses are configured such that they can be connected to input/output lines I/O leading from the memory.
Previous designs of DRAMs have been provided with at least one redundant data line per group or a complete redundant group. A group in this case comprises a number of data lines.
In the case of this design of redundancy within a group, interconnection between the groups is not provided. This approach has the disadvantage that the maximum possible number of data lines that can be replaced within the group corresponds to the number of redundant lines per group.
In modern semiconductor memories, in which advancing technology is leading to smaller and smaller structures, contamination or other disruptive parameters such as, for example, layer thickness fluctuations in the fabrication process constitute a cause of defects which extend over a plurality of data lines or memory cells.
Thus, an areal defect, a so-called cluster defect which extends over a plurality of bit lines or memory cells can cause the on-chip redundancy devices within the memory chip which are designed according to the prior art to rapidly come up against their limits. In the case of a cluster defect, the number of data lines that may be affected in a group may be more than the number of redundant lines available in the group. In such a case, the entire memory chip can no longer be used, resulting in a total failure.
Moreover, defects, and in particular including cluster defects, of the local data lines internal to the memory or of the data lines are not precluded even in the course of fabrication. As a result, whole groups of local data lines which are assigned to the defective data line fail and have to be replaced. In such a case, the system of redundancy data lines limited to a group fails completely.